解决tcpdump -w 的写缓存不实时写文件的问题解决

问题:
解决tcpdump -w 的写缓存不实时写文件的问题解决

解决方式: --待测试
tcpdump -w file直接写文件，而不适用操作系统写缓存方式

 --packet-buffered
              If the -w option is not specified, make the printed packet  out‐
              put  ``packet-buffered'';  i.e.,  as the description of the con‐
              tents of each packet is printed, it will be written to the stan‐
              dard  output, rather than, when not writing to a terminal, being
              written only when the output buffer fills.

              If the -w option is specified, make the saved raw packet  output
              ``packet-buffered'';  i.e.,  as each packet is saved, it will be
              written to the output file, rather than being written only  when
              the output buffer fills.

              The  -U  flag will not be supported if tcpdump was built with an
              older version of libpcap that lacks the pcap_dump_flush()  func‐
              tion.